Season both sides of fish steaks with salt and pepper to taste. In a large frying pan or skillet on medium heat place in oil. When oil is hot place fish in frying pan and fry until lightly brown on both sides. When both sides are lightly browned lower heat to medium/low and let cook uncovered for 15 minutes -midway through cooking time(6-1/2 - 7 minutes), turn over fish to the other side and continue to cook.
Meanwhile slice onions,then peel and lightly crush the garlic.
After fish is finished cooking (15 minutes later) remove fish from pan to a papertowel lined plate.
In a deep glass jar with a cover or a deep glass plate that you can cover, place in oil, vinegar, bay leaves, peppercorns, oregano and garlic. (NOTE: During pickling, garlic may turn a greenish color--do not be alarmed, this is expected and it will not affect the flavor of this dish.) Then add in 1/4 of onions and 1(one) layer of fish --then place in more onions on top-- repeat process until finished with onions and fish. Mix or shake jar until onions and fish are coated with vinegar and oil mixture. Place in refrigerator for at least 24 hours mixing or shaking jar every 5-6 hours. This will keep in the fridge for weeks.